(1) Field of the Invention
The present invention relates to communication networks in general and more particularly to the protocols which are used to transport information within the networks.
(2) Prior Art
The use of computer network systems for processing and transmitting data is well known in the prior art. A typical computer network system consists of at least one host computer running under some type of operating system, communication controllers, a communication medium and a plurality of end users (terminals, printers, displays, etc.). The host computer is connected, via communication media, to either a communication controller or an end user terminal. The communication controller interfaces with other communication controller or end user terminals via the communication medium. The communication medium may be telephone lines, channels, satellites, etc. By entering a request at a user terminal, a user may extract data from the host computer. Similarly, a user may enter information on a terminal and have it transmitted to the host computer for processing and/or to another terminal in the network.
In addition to the physical structure, the prior art computing systems are controlled by a system architecture which ensures the orderly flow of information through the system. The prior art describes several types of architectures. For example, an overview of the architecture used in computer networks is given in an article entitled, "Computer Network Architecture," by S. Wecker in Computer, September 1979. Another overview, including a description of System Network Architecture (SNA) is given in an article entitled, "An Introduction to Network Architectures and Protocols," by P. E. Green and printed in the IBM System Journal, Vol. 18, No. 2, 1979. In these articles, the various computer networks such as SNA, DMA, ARPANET, etc. are described by means of hierarchical architectural layers, where the lowest layer relates to the physical communication lines interconnecting various user nodes of the network and where the highest level concerns the conversation per se between the various end users of the network.
In an attempt to standardize network architecture, the International Organization for Standardization (ISO) has adopted a model which is described by Herbert Zimmerman in an article entitled, "OSI Reference Model--the ISO Model of Architecture for Open Systems Interconnections," IEEE Transactions on Communications, April 1980. The model architecture consists of seven layers, namely: physical, data link, network, transport, sessions, presentation and application layers. The present invention mainly concerns the presentation service layer of SNA which relates to the information unit which is used to transmit information between two end users.
The prior art utilizes "Information Units" with different type formats for carrying messages through the network. Notwithstanding the type of format, the prior art Information Units are plagued by a common problem; namely, how to identify the length of a particular message and how to distinguish between control information and user data. The control information is used by the presentation layer while the user data is for an end user.
One prior art solution is the use of delimiters to bracket the message. A beginning delimiter is used to signify the beginning of a message and an end delimiter is used to signify the end of a message. In addition to the delimiter and identification marker is used within the message to differentiate between "user data" and "control information."
Although the above information unit and technique works well for the intended purpose, it is not very efficient. This is so because the receiving node must analyze the message to determine the type of information. The analysis takes time which tends to slow down the performance of the overall system. Moreover, the prior art information unit is not easily adapted to transport control and/or user data in a common data stream. Finally, there are several applications in which predefined delimiters cannot be used to signify the start and end point of user data.